1. Field of the Invention
This invention relates to aircraft gas turbine engine turbine blade tip shrouds and seals and, more particularly, to cooling the shroud and tip.
2. Discussion of the Background Art
Gas turbine engines frequently employ tip shrouds on individual airfoils to limit blade amplitudes when vibrating in a random manner and to guide fluid flow over the airfoils. This is particularly true in the low pressure section of a gas turbine engine. Neighboring shrouds abut in the circumferential direction to add mechanical stiffness. When a series of such assemblies are mounted together, the shrouds define in effect a continuous annular surface. Circumferentially opposite edges of the shrouds in the circumferential direction are provided with abutment faces and are designed to introduce to the assembly desired constraints.
Circumferentially extending seal teeth extend radially outwardly from the shrouds to engage seal lands to seal the gas flowpath between the shrouds and casing surrounding the rotor. The seal lands typically are in the form of a honeycomb covered stator shroud.
Gas turbine engines typically include cooling systems which provide cooling air to turbine rotor components, such as turbine blades, in order to limit the material temperatures experienced by such components. Prior art cooling systems usually acquire the air used to cool turbine components from the engine's compressor, after which it is diverted and subsequently directed to the turbine section of the engine through an axial passageway.
Low pressure turbine blades typically are not cooled. High pressure turbine blades which are typically cooled do not have deflection restraining tip shrouds. Supersonic high performance engines are being developed for long distance supersonic operation, such as for the High Speed Commercial Transport (HSCT) engine program. The low pressure turbine blades in the low pressure turbine section are exposed to high temperatures for long periods of time over most of the flight envelope with the engine operating at high power engine settings. It is also desirable to have a low engine weight and engine length.
High speed engines require better cooling techniques than those presently used. One exemplary engine for a high speed civil transport employs a low pressure turbine in close proximity to a high pressure turbine discharge. Furthermore, the engines mission requires long term exposure of the low pressure turbine to very high temperatures at high power engine settings. Aircraft gas turbine engine designers constantly strive to improve the efficiency of the gas turbine engine as well designing an engine which is low weight and short. The use of cooling air increases fuel consumption and, therefore, it is highly desirable to minimize the amount of engine work used to produce the cooling air.